This invention pertains generally to a plier-type tool somewhat similar in purpose and appearance to those in the prior art known as water pump pliers or slip-joint pliers. The invention more particularly pertains to an automatic slip-joint plier-type tool which will slidably adjust to, and then pivotally grip against, any workpiece the size of which is within the range of the tool's jaws.
Heretofore, two U.S. patents which disclose an automatically self-adjusting plier-type tool. In U.S. Pat. No. 4,651,598, the basic structure and function is disclosed for self-adjusting utility pliers which, by one-hand manipulation, automatically slide the lower jaw relative to the upper jaw to contact the workpiece whereupon the sliding action of the lower jaw converts to a pivoting action to exert positive gripping force against the workpiece as continued manual pressure is exerted against the tool's handle ends. In U.S. Pat. No. 4,662,252, improved alternative embodiments are disclosed for the construction of such a tool at significantly reduced cost.
While the tools and the features thereof which are described and illustrated in the aforementioned patents constitute a significant contribution to the art of tools and instruments, further experimentation and development relating to the basic operational concept in a self-adjusting plier-type tool have led to the conception of significant cost saving and operational improvements as herein disclosed.
The basic operating principle of the automatic self-adjusting plier tool is first disclosed in the aforementioned U.S. Pat. No. 4,651,598, wherein the basic tool structure includes two rigid body members movably joined at their neck portions in a scissors-like arrangement to be, during the use of the tool, both slidable and pivotable relative to each other. These body members have angled jaw ends in opposed relation which constitute the working end of the tool and handle ends constituting the gripping end of the tool. The structure of the tool which enables the self-adjusting function by one-hand manipulation includes an elongated slot in the neck portion of the major body member, and a fastener or pivot post projecting from a fixed position on the neck portion of the minor body member and extending through the elongated slot of the major body member.
For general reference and an understanding of this disclosure, the major body member of the self-adjusting tool can be referred to as member A, and the minor body member, from which the pivot post projects, can be referred to as member B. Accordingly, in the aforementioned basic U.S. Pat. No. 4,651,598, one means of attaining the necessary biasing function that normally causes the jaws to slide open is the provision of a wire compression spring disposed longitudinally on member A to exert a pushing force against an end of the control arm and thereby cause member B to slide relative to member A. Although the use of the aforementioned arrangement sufficiently demonstrates the self-adjusting principle, it was found in the early development of the tool that a more positive action could be obtained by enhancing the biasing means through the addition of a spring carried on member B which is adapted to exert a secondary force on the control arm to normally cause the control arm to pivot on member B toward the jaw end of the tool whereby the sliding opening action becomes a motion of member A relative to member B. Then, the primary purpose of the longitudinal compression spring on member A is to effect a translation of force through the control arm, when the jaw ends contact a workpiece, to shift the pivot post on member B laterally in the longitudinal throat portion slot of member A whereby the pawl or camming member carried on the pivot post engages along a long edge of the slot. Hence, the longitudinal spring functions to convert the jaw-closing sliding action, upon workpiece contact, to a continuing jaw-rotating or pivot action between the joined body members.
Subsequent to the development of the operating principle for the self-adjusting plier-type tool, various arrangements for the biasing means were devised, utilizing springs of different configurations and location to provide the necessary forces between the members A and B through the interconnecting control arm. One purpose in altering the biasing means arrangement was to place the spring components fully inboard in a concealed and protected disposition while increasing the operating efficiency of the tool. Different problems were encountered in spring selection and securement in obtaining the desired biasing function, depending on whether the members A and B were to be solid, drop-forged members or stamped and shaped from relatively thin sheet metal.